Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$88.67	13.599%	$100.7282	$100.73	$100.75	$100.70
Purchase #2	$217.97	6.801%	$232.7941	$232.79	$232.80	$232.80
Purchase #3	$126.93	7.123%	$135.9712	$135.97	$135.95	$136.00
Purchase #4	$114.39	5.428%	$120.5991	$120.60	$120.60	$120.60
Purchase #5	$37.34	13.319%	$42.3133	$42.31	$42.30	$42.30
Purchase #6	$138.52	10.112%	$152.5271	$152.53	$152.55	$152.50
Purchase #7	$130.69	12.434%	$146.94	$146.94	$146.95	$146.90
7 purchase totals =	$854.51		$931.8730	$931.87	$931.90	$931.80